There are large individual differences in drug abuse vulnerabilities among humans that are likely to display genetic as well as environmental components. During this year, these investigators continued to explore possible roles of allelic variants at candidate gene loci in possibly contributing to human individual differences in drug abuse vulnerability, made substantial progress with genome scanning approaches to identifying previously-unanticipated gene loci conferring drug abuse vulnerabilities, validated pooling strategies for simple sequence length polymorphisms, described the limitations of the sibship collections possible in the intramural setting, and made major advances in providing simulations and modeling for the power of genome- wide and focused association/linkage -disequilibrium based genome scanning. This work identified DRD4 gene variants associated with substance abuse vulnerability, but no association with candidate markers at the DRD3 locus, and identified candidate chromosome 11 and 2 regions that contain interesting candidate genes. - complex genetics drug abuse candidate gene genome scanning - Human Subjects: Interview, Questionaires, or Surveys Only